Need to fix your car's air conditioner? We are a team of ASE certified
mechanics that have created this guide for you so you can understand how the
system works and what to look for when it doesn't. We also have included popular
repair guides with videos which will help you stream line your repairs or see what you are paying
for when taking your car in to a repair shop. Let's jump right in!
When looking under the hood at your car's air-conditioner it might seem
complicated but it's not. Once you know how it delivers cold air you will see
it's really quite simple. Your heater and air conditioner (HVAC) does three
jobs; cool the interior of the car, heat the interior up and defrost the
windshield. All three modes work together as a complete system. The climate
control system is controlled by a main computer which houses the controls for
the system and sits in the dash in most cases.
This computer gives commands to the compressor to start pressurizing the refrigerant
along with the blend door actuators which direct air flow from the floor, mid and
defrost vents. These air door actuators also control air temperature by mixing the hot air
from the heater and the cold air from the AC. When one part of the system fails to operate like the air conditioner then
one part of the system stops working in this case the cold air.
The AC system has four basic parts: A compressor, which is powered by the
engine using a serpentine belt.
On hybrid cars the compressor is electrically powered and does the same
operation. A condenser which is located in front of the engine radiator and cools the refrigerant
from the compressor before it heads to the evaporator located inside the vehicle.
This is where the high pressure liquid is released into the evaporator
as a low pressure gas and where the coldness is created.
The blower motor then circulates the air throughout the interior.
Before you start doing repairs on the system it's a good idea to
see how the
a/c system works.
Before You Begin
Start with the car on level ground with the transmission is park and the
emergency brake set. The engine should be off, but warm. Wear safety goggles and gloves
to protect against injuries. Never loosen or undo any hoses or fitting before
the system of refrigerant. The system does contain a slight amount of oil
which can be expelled while discharging.
You will see tools and supplies used in the following guides that you will be
able to find throughout and at the end of this article, also a list of specific
repair manuals. One thing to remember is all air conditioner systems work on the
Okay, now that you have had a crash course on how the system works let's approach
this problem like a mechanic would.
Why Isn't My Air Conditioner Working?
If air is not blowing from the vents it is not the problem of the refrigerant
recycling system (A/C) and can be attributed to the blower motor or a vent control
actuator. Here is how to tell which; start the engine and turn the air conditioner
on. Next, move the fan setting from the highest to the lowest. If you can hear nothing
it is a problem with the blower fan.
If you can hear the fan but no air is forced through the vents, or if the air
is being generated from the wrong vents this is an
If air is blowing from the correct vents but is not cool (no cold air - blowing
warm air) continue down the guide.
When the air conditioner is switched on three things begin to happens, the
compressor, blower motor and vent actuators all receive an electrical signal to
turn on. This causes the compressor clutch to engage while working the internal
parts of the compressor pump. This pumping action compresses the refrigerant so
it can circulate around the system. The following step are presented in
order of popularity.
Step 1: Check the A/C System Charge
As your vehicle ages the refrigerant level should be maintained and added too
insuring that the system stays full. Because this system is pressurized kind of
like a tire it will need to be recharged as it ages. Recharging the system is
not to difficult and can be done in about 20 minutes.
If the system is low then you can
recharge and monitor how long the charge lasts. If the system lasts up to
6 months then another recharge might outweigh repairing the system which you can
do for about $35.00 yourself. A sign of a
system being low on charge is that it will produce white vapor from the vents
much like your home freezer. This is because the pressure drop inside the
evaporator is to excessive causing it to "ice up".
Recharging the a/c system will fix this problem.
To check the system's "state of charge", connect a gauge or charge kit to the
low side hose service port to read the static pressure.
This will show the pressure in the system. If the system is flat there is a
that must be discovered and repaired before recharging the system.
If the system is full and the static pressure (engine off) is between 70 and 90 psi then continue down the guide of
checking the system.
Step 2: Check the Compressor Operation
In this image the engine is running but the clutch is
not engaged. With the system on this can mean one of two things, first the
system is low on charge and so the compressor will not turn on via a pressure
switch located somewhere on the low pressure side of the system. Or there is an
electrical problem of some kind ie: blown fuse, relay and clutch engagement coil or climate control
computer shorted. If when you turn the air conditioner on there is a loud
screeching noise the
compressor has locked up and needs replacement.
Before we keep going there is an additional style of compressor that are
featured on German cars (BMW, Mercedes Benz and Volkswagen) which does not have
a clutch. One of these compressors is featured on the image below in which there
is no clutch and no wires to an activation coil.
As you can see the portion of the pulley hub where the clutch would be located
is directly bolted to the input shaft of the compressor. These compressors have an
internal valve which is located at the rear of the compressor
to begin the process when activated. For these cars there will be one variable in testing which
we will get to further down in the guide.
On clutch style compressors with the system still on and set to the coldest
setting and highest fan speed locate the compressor. Using a flashlight and
inspect the clutch operation it will be doing one of two things; first, it will
be cycling on and off which means the
system is low on charge or the condenser fan is not operating or there is
blockage in the expansion or orifice tube.
If the clutch is doing nothing then its time to connect a gauge or charge kit
to see if the system is completely flat or is just so low on charge. When the
system is low or overcharged a pressure switch tells the compressor when to shut
down to avoid damage. On internal valve compressors i.e. German cars you must use a test light to see if the signal wire
is getting power or not. This style of system does not cycle when it's low it
just shuts down so its best to check the systems charge.
Step 3: Check the Condenser Fan
Start the engine and set the air conditioner to its coldest setting. The
first thing to look for is the condenser fan being on (if equipped). This fan
should turn on within a minute of the AC system being switched on. If this fan
is not on then this is a problem that must be checked out. If the vehicle is
rear wheel drive and has a mechanical fan look to see if the fan is "freewheeling"
which is an indication of the fan clutch being bad and needing replacement. The
condenser must have air being pulled or pushed through it for the system to
Step 4: Check the Climate Control Electrical System
Observe the climate control panel to see if there are any lights
that are blinking which indicates there is some kind of failure in which a code
must be read. Each method of retrieving these codes is different to each manufacturer. These
codes will guide you to the circuit or system that is having a problem. If
everything looks okay on the panel or the panel lights are out completely please continue
down the guide.
Locate the car's fuse panel under the dash or power distribution center under
Using a test light check all related fuses such as the BCM, climate control,
heater, blower motor and for the air conditioner. You can use your car's owner's
manual to help locate the fuse.
If the new fuse blows once it's been replaced there is a short in the system.
Most of the
time this short can be related to the
clutch coil in which case it needs to be
If all related fuses are okay the next part in the system that has a high
failure rate is the a/c relay. This relay supplies main power to the compressor
via the system fuse. Locate the relay in the fuse panel or power distribution center
using the owners manual.
check the terminals
of the relay for power and ground and then replace the relay to recheck the system. You can swap this
relay for a similar one in the car such as the power windows or door locks to
test it, many of these relays are the same.
A pressure sensor is used to measure the amount of refrigerant is in the system.
When this sensor goes bad the compressor will not turn on. To test this sensor
remove the wiring connector and insert a jumper wire between the two terminals
of the connector. If the compressor turns on the sensor is bad or the system is
low or overcharged. If nothing happens use a
test light to see if there is 12 volts
at one of the wires. If no power is present suspect the climate control computer being bad.
If you have perform all of this tests and the system is still not working a pin
to pin voltage and continuity check is in order. This test sounds harder than it
is, using a wiring diagram for you car you basically you are required to
each wire for power or ground and then continuity to make sure each wire is
engine is overheating or low on coolant the air conditioner will be weak
or not work at all. If you have been driving for sometime and you noticed the system stops working
the first thing to check it the engine temperature gauge or warning light.
Watch the Video!
Tree leaves, plastic bags and dirt can get logged in the condenser hindering
the systems performance. Remove any obstructions such as plastic bags from the
condenser area. Also use a garden hose to clean the condenser with a high
pressure nozzle from time to time. This works really well and helps the air
conditioner work more efficiently. The compressor is the main mechanical part of
the system which is driven by the engine's serpentine belt. This belt should be
in good working order and replaced if worn.
Some cars are equipped with the cabin air filter which is much like an engine
air filter that can plug causing restricted air flow. This filter should be
replaced when air flow becomes restricted.
If repairs have been made, the system will need to be
vacuumed down and recharged to remove damage causing moisture. If you don't
vacuum the system the A/C will not be as cold because of the air that is trapped inside
the system once it has been opened.
There are various tools and supplies you will need throughout this article. We
have created a list for you which are easily obtained if you do not have them
Tools and supplies needed for air conditioner repair
You will also need replacement parts such as a fuse or a relay. We have created a guide that will inform you as to where to go
to get the best deal and quality.
Learn more: Air
conditioner replacement part
To see more specific information about your particular vehicle check out our
repair manual information guide.
Air conditioner repair manual
If you have any
questions about car air conditioners please visit our forum. If you need
car repair advice please
ask our community of mechanics are are happy to help.